The invention relates to a time base correction apparatus using a variable signal delay device such as a CCD (charge coupled device).
A reproduced video signal obtained from recording/playback apparatus such as a VTR (video tape recorder) usually contains jitter-drift components. For correcting the jitter-drift components, a time base correction apparatus using a variable delay device such as a CCD (charge coupled device) is considered to be effective. As one of those apparatuses, there is a single delay apparatus which is disclosed in Japanese Patent Public Disclosure No. 52349/77. This prior art delay apparatus uses a signal delay element such as a shift register, a BBD or a CCD for effecting the time base correction. When the CCD, for example, is used for the signal delay element, the time base correction is performed through the control of a delay time by changing a clock frequency for transferring an input signal of the CCD. In the time base correction apparatus based on such a time correction idea, the signal transfer efficiency is degraded as the transfer clock frequency becomes high. In other words, a delayed output signal level of the CCD is reduced as the transfer clock frequency becomes higher. Additionally, the prior time base correction apparatus has a disadvantage that a DC level and an amplitude of the CCD output signal vary with a change of the transfer clock frequency caused by the time-delay control. Thus, the apparatus is effective for the correction of the jitter-drift components attendant with a time or phase variation, but is ineffective for the correction of the DC level and amplitude variations. This means that the amplitude and the DC component of the CCD output signal may vary in synchronism with the period of jitter-drift. When the time base correction apparatus is applied to a VTR, for example, a video output signal applied from the VTR to a monitor TV accordingly varies to possibly cause flicker noise to appear on a CRT screen.